Arkosic Sandstones Research Articles

The influence of the cataclastic matrix on the petrophysical properties of deformation bands in arkosic sandstones

This study investigates how the intensity of the cataclasis deformation mechanism influences petrophysical properties, such as pore diameter, grain size, porosity, and permeability, in deformation bands of arkosic sandstones and conglomerates affected by normal fault zones in the Rio do Peixe Basin, Brazil. We analysed in detail the cataclastic matrix within the deformation bands, defined as the amount of fine particles (<1000 μm) generated by grain crushing that surrounds the coarse particles. We collected data in deformation bands exhibiting different textures such as protocataclastic, cataclastic, and ultracataclastic textures, and we performed structural, microstructural, and petrophysical analyses to establish the geometry, temporal relations, kinematics evolution, and deformation mechanism responsible for the formation and evolution of the deformation bands. Deformation bands evolved progressively with increasing grain comminution, which results in different cataclastic textures within a normal fault zone. These textures influence petrophysical properties, mainly porosity. For example, an increase in the cataclastic matrix generates a decrease in macropores, affecting the pore access. The arkosic and arkosic-lithic sandstones present a more selective intragranular fracturing of feldspar grains than of quartz grains. This fact indicates some degree of mineralogical control on the grain size distribution and porosity. As a result, in the ultracataclastic textures, quartz clasts are relatively well preserved, and feldspar grains are almost completely destroyed. Our study indicates that it is possible to estimate the relative porosity reduction of deformation bands by analysing the amount of cataclastic matrix. These results could greatly influence our understanding of the reservoir properties in faulted arkosic sandstones.

The Hushoot Shiveetiin gol section (Baruunhuurai Terrane, Mongolia): sedimentology and facies from a Late Devonian island arc setting

A Late Devonian to (?)Early Mississippian section at Hushoot Shiveetiin gol in the Baruunhuurai Terrane of the Central Asian Orogenic Belt (CAOB) exposes large parts of cyclic Famennian shallow-water siliciclastic shelf deposits composed of siltstones, sandstones, shales, volcaniclastics, and intercalated autochthonous carbonates. The youngest part of the section, possibly Early Mississippian, is represented by arkosic sandstones with large plant remains. The facies reflects a range from shallow-intertidal to outer ramp settings. In terms of conodont stratigraphy, the Hushoot Shiveetiin gol section ranges from the Palmatolepis minuta minuta Biozone to at least the Palmatolepis rugosa trachytera Biozone. Hiatuses of several conodont biozones occur due to the facies setting (erosion and reworked sediments which are recognized by reworked conodonts) rather than thrusting or folding. The environmental setting was characterized by coeval subaerial volcanism resulting in numerous pyroclastic deposits. The depositional environments and intense volcanic activity at the Hushoot Shiveetiin gol section limited the stratigraphic distribution, abundance, and diversity of many elements of the fauna such as brachiopods. Ostracods were very abundant and diverse through many parts of the section. Although limited in stratigraphic distribution, the crinoid fauna is the most diverse Palaeozoic fauna collected from Mongolia to date and supports the hypothesis that the CAOB was a biodiversity hotspot in the aftermath of the Frasnian–Famennian extinction event.

Vertebrate Trace Fossils: the Congo's Brasilichnium mammaloid fossil footprints

The ichnogenus Brasilichnium, with its ichnospecies type Brasilichnium elusivum, was established for a very common and abundant kind of tracks from the Brazilian aeolian Botucatu Formation in Parana Basin. It is nowadays a recognized ichnogenus on several continents. On the South American continent, it was found in Brazil and Paraguay. On the North American continent, it was found in Mexico and in several localities of the United States. In Asia it was found in Korea and China; and in Africa it was found in Tunisia, Namibia and Lesotho; while in Europe it was found only in Italy. A new occurrence of this ichnogenus (and also of the ichnospecies Brasilichium elusivum) is herein announced from Cretaceous arkose sandstones, at Kinshasa, Democratic Republic of Congo. Three slabs with several mammaloid footprints attributable to this ichnogenus were found in Kinshasa, in red sandstone slabs cladding facades of pre-independence (1960) buildings. These slabs were and are quarried at the NW margins of Kinshasa along the left banks of the Congo River, in the districts of Kimbwala and Mbudi. This material can be attributed to the Loia Formation (Berriasian-Aptian). These are the first tetrapod tracks in the Democratic Republic of Congo, and possibly in all of Central Africa. It is important to keep on surveying for tracks in the quarries and on the facades of buildings in Kinshasa, in order to increase the potential use of ichnology to environmental and palaeogeographic reconstructions.

Sedimentology of Shahejie Formation, Bohai Bay Basin: a case study of Es1 member in Nanpu Sag

The Es1 sandstone is a fruitful hydrocarbon zone of Eocene Shahejie Formation. Therefore, the present study comprises the subsurface facies analysis established on the description of seven wells. Methods include core observation, thin section petrography, scanning electron microscope (SEM), cathodoluminescence (CL), and X-ray diffraction to evaluate the microfacies, lithofacies, and rock characteristics. Two microfacies of lithofacies have been established as sandstone microfacies and mudstone microfacies on the basis of grain size. Among them, sandstone is further divided into four sub-microfacies on the basis of microscopic studies, rock fragments and mineral composition, which are arkose sandstone, lithic arkose, feldspathic litharenite, and litharenite. These microfacies consisting quartz, feldspar as abundant detrital grains followed by rock fragments and micas, whereas calcite, ferro-calcite, quartz overgrowth, and clay are the main cement. The Es1 sandstone consists of good primary porosity and permeability as well as good secondary porosity caused by fracturing and dissolution of unstable minerals that enhance the reservoir quality. Whereas cementation and compaction reduce the reservoir characteristics. Studied formation divided into five lithofacies including conglomerate sandstone lithofacies, medium to coarse-grain sandstone lithofacies, fine sandstone lithofacies, siltstone lithofacies, and mudstone lithofacies. Core observation, sedimentary structures, facies sequences of the well log, and sedimentary composition reveal that Es1 deposited into the lacustrine delta fan depositional environment. Rock grain size indicates that Es1 contains mixtures of grains including pebbles, sand-size as well as minor silt and clay size. Grain size varies from conglomerate to clay size. The Es1 sandstone was deposited in braided river (conglomerates sandstone), channel bar, lacustrine, fluvial channel (massive bedding, cross-bedding, and graded bedding sandstone), deltaic, and flood-plain (siltstone and mudstone) sedimentary environment. It is concluded that higher transport energies in channels deposited coarse-grain sediments in shallowest part of the lake setting. However, the energy decreases towards greater depth which deposited mudstone in central part of the lake.

Geochemistry of oxidic soils developed from different parent rocks in the Limpopo Province, South Africa

The study assessed the geochemical characteristics of oxidic soils developed from different parent rocks in the Limpopo Province, South Africa. The main aim of the study was to assess the overall soil quality in the study area. Soils and fresh rock samples were collected from four different parent rocks (basalt, granite, gneiss and arkosic sandstone) in Limpopo Province for geochemical analyses using X-ray fluorescence (XRF) spectrometry and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analytical methods. The geochemical compositions of the soils showed relative enrichment of Fe2O3, TiO2, CaO, K2O, MgO, MnO, and Na2O (except for CaO, K2O, MgO, MnO, and Na2O in soils developed from basalt). The chemical index alteration (CIA) values varied between 55 and ≈100, which suggest a low to very high degree of chemical weathering. The Al2O3 – (CaO* + Na2O) – K2O (A-CN-K) and Al2O3 – (CaO* + Na2O + K2O) – (FeO + MgO) (A-CNK-FM) diagrams for the different soils also support these observations. Trace elements were significantly enriched in soils developed from basalts and gneisses, but were minimally enriched in soils developed from granites and arkosic sandstones based on their enrichment factors. The ecological risk assessment of the soils based on risk index (RI) indicated a low risk in decreasing order of soils developed from basalt > gneiss > arkosic sandstone > granite, respectively.

Displacement-dependent microstructural and petrophysical properties of deformation bands and gouges in poorly lithified sandstone deformed at shallow burial depth (Crotone Basin, Italy)

We present the results of meso-and micro-structural analyses performed on fault-related soft-sediment deformation structures affecting poorly lithified, high-porosity siliciclastic sediments in the Crotone Basin, Southern Italy. The investigated extensional fault zone has a total displacement of ~90 m and juxtaposes marine clayish sediments in the hanging wall against arkosic to lithic arkosic sandstone in the footwall. In the footwall damage zone, deformation is achieved by a network of conjugate deformation bands, whereas the foliated fault core hosts cm-thick gouges. Deformation bands and black gouges accommodated displacement between 0.2 and 20 cm. Microstructural observations and quantitative image analysis pointed out that particulate flow operated during the early stages of faulting, followed by cataclasis after significant porosity loss. Mineralogy of clasts controlled grain-scale deformation mechanism: following this, feldspar experienced extensive intragranular crushing, while quartz grains were deformed mainly by splitting and abrasion. Permeability of pristine sandstone spans from 5.4 × 104 to 1.4 × 105 mD, while inside deformation bands is reduced by 1-2 orders of magnitude, reaching 3-4 orders of magnitude within fault gouges. Permeability drop inside the fault zone is related to the accommodated displacement along each deformation structure, potentially leading to hydraulic compartmentalization of high-porosity sandstone reservoir.

Late Paleozoic detrital history of eastern Gondwanaland: petrofacies and detrital geochronology of Permo-Carboniferous intracratonic sequences of the northwest Bengal Basin

ABSTRACTPermo-Carboniferous Gondwanan sequences have been reported from several isolated basins of Peninsular India. These siliciclastic sequences were preserved in several intracratonic basins in northwest Bangladesh. Sandstone petrography, heavy-mineral assemblages, mineral chemistry, and 40Ar/39Ar geochronology of sediment cores were used in this study to decipher the provenance history of Gondwanan sediments at two localities (Khalashpir and Barapukuria). Petrographic studies suggest that these sequences are mostly immature and poorly sorted arkosic sandstones (Khalashpir-Qt60F27L13, Barapukuria-Qt52F31L17), with compositions ranging from quartzarenite to litharenite. Among lithic fragments, sedimentary types are abundant. Heavy minerals are volumetrically rare and of low diversity in sediments of northwest Bangladesh. Garnet geochemistry indicates that metamorphic grades in the source terranes were of the amphibolite to granulite facies. Laser 40Ar/39Ar ages for single crystals of detrital muscovite from the deepest drilled Gondwanan sequences yielded the broadest age range, with a dominant mode at circa 515 Ma and lesser clusters of ages at circa 550, 570, and 600 Ma. The other two shallower samples are dominated by ages with similar single modes at circa 495–500 Ma. The oldest muscovite crystals may have been derived from the adjacent Indian craton and/or the Meghalayan craton. Younger muscovite crystals may have been contributed from the Pinjarra Orogen, formed during episodes of Neoproterozoic to early Paleozoic collision among India, Antarctica, and Australia.

Characterization of sub-seismic resolution structural diagenetic heterogeneities in porous sandstones: Combining ground-penetrating radar profiles with geomechanical and petrophysical in situ measurements (Northern Apennines, Italy)

Deformation bands and structurally-related diagenetic heterogeneities, here named Structural Diagenetic Heterogeneities (SDH), have been recognized to affect subsurface fluid flow on a range of scales and potentially promoting reservoir compartmentalization, influencing flow buffering, and sealing during production. Their impact on reservoir hydraulic properties depends on many factors, such as their permeability contrast with respect to the undeformed reservoir rock, their anisotropy, thickness, geometry as well as their physical connectivity and arrangement in the subsurface. We used the Ground Penetrating Radar (GPR) for detection and analysis of the assemblage of deformation bands – carbonate nodules, in high-porosity arkose sandstone in Northern Apennines of Italy. 2D GPR surveys allowed the description of the SDH spatial organization, their geometry, and their continuity in the subsurface. Petrophysical (air-permeability) and mechanical (uniaxial compressive strength) properties of host rock, deformation bands, and calcite-cement nodules were evaluated along a 30-m thick stratigraphic log to characterize the permeability and strength variations of those features. The assemblage “deformation bands – nodules” degrade porosity and permeability and produce a strengthening effect of the rock volume, imparting a strong mechanical and petrophysical heterogeneity to the pristine rock. Different textural, petrophysical, and geomechanical properties between deformation bands, nodules, and host rock result in different GPR response (permittivity). Thus, GPR response could be used to extend outcrop data (petrophysical and geomechanical) of SDH to 3D subsurface volumes in a way to reconstruct realistic and detailed outcrop analogs of faulted aquifers and reservoirs in porous sandstones. • GPR effectively detects deformation bands and diagenetic heterogeneities in sandstones. • Deformation bands and cement nodules show high compressive strength and low permeabilities. • GPR response correlates with petrophysical and geomechanical rock properties. • An improved reservoir analog is obtained from integrating outcrop-based and GPR data. • Deformation bands and nodules impart anisotropy to the host rock.

Detrital zircon U-Pb dating in the southern Hefei Basin: Evidence for exhumation of HP-UHP rocks of the Dabie Orogen

The Hefei Basin of eastern China developed in response to uplift of the Dabie Orogen, and zircon dating can be used to assess the exhumation history of the orogen. Zircons were collected from samples of the Lower Jurassic Fanghushan Formation and Middle Jurassic Sanjianpu Formation in the southern Hefei Basin, and mica-quartz schist and biotite granite gneiss from the Susong Complex of the Dabie Orogen. The zircon U-Pb dating was undertaken using laser ablation-inductively coupled plasma-mass spectrometry. The detrital zircons from conglomerates of the Fanghushan Formation and from clasts within the conglomerates have age-frequency distributions with the main clusters between 2.0 and 1.8 Ga, similar to age data of the Susong Complex. On the other hand, the zircons of the Fanghushan Formation do not show the age cluster at 1000-900 Ma that characterizes zircons in the underlying metasediments of the lower Paleozoic Foziling Group. A cluster of Triassic zircon ages also appears in the arkosic sandstones of the Fanghushan Formation. These data indicate that the provenance of the Fanghushan Formation was a mixture of high-pressure (HP) and ultrahigh-pressure (UHP) Triassic metamorphic rocks, Paleozoic magmatic rocks, and the Susong Complex, but not the lower Paleozoic Foziling Group even though it directly underlies the sediments of the Hefei Basin. Two samples from the Sanjianpu Formation show zircon age clusters at 797 and 791 Ma (middle Neoproterozoic) and 226 Ma (Triassic), and again, these are markedly different from the age clusters that characterize the Foziling Group. It seems, therefore, that despite the Foziling Group being at the surface in the underwater depositional area of the Hefei Basin, it was not exposed in the source area of the Hefei basinal sediments during the Jurassic, and there are two possible reasons for this. First, the exhumation of the Dabie Orogen was directed partly towards the north, in the process of which some of the Foziling Group was covered. Second, the Susong Complex rocks became involved in the development of an accretionary wedge, thus covering some of the Foziling Group during the process of subduction.

Petrofacies of Eocene sand injectites of the Tumey Giant Injection Complex, California (USA)

The forearc succession of Great Valley Group in Central California provides some of the best examples of giant sand injection complexes in the world and is therefore considered valuable analogues for injectite systems in the subsurface. Several sand injection complexes are well described in the outcrop and subsurface, however the petrographic characteristics of injectites are still poorly documented. In this paper, we present the results of an integrated study of field observations, quantitative and qualitative sandstone petrography, provenance, and petrofacies analysis of the Tumey Giant Injection Complex (TGIC) in order to understand its lithostratigraphy and petrological evolution, and its impacts on reservoir petrofacies characteristics and fluid migration. The TGIC intrudes into a 450 m thick deep-water succession of slope mudrocks and sandy channel-fills of the Kreyenhagen Shale (Eocene), forming an interconnected network of sandstone sills, dykes and injection breccias. The complex generated a horizontal and vertical plumbing system for fluid migration, connecting isolated sandy channel-fills among low-permeability mudrocks. The primary detrital composition, diagenetic products, microtextures, and provenance signatures allowed for the definition and discrimination of depositional and intrusive petrofacies and their genetic relations. Petrofacies associations confirm that the gypsum-cemented feldspathic litharenites from the Kreyenhagen Shale channel-fills are the only source for the injection complex. Eodiagenetic compaction and extensive gypsum cementation reduced the primary porosity of the complex, while telodiagenetic dissolution of autigenic constituents formed pervasive secondary porosity. The underlying calcite-cemented arkosic sandstones of the Lodo and Domengine formations acted as barriers for fluid flow, aiding lateral fluid migration and overpressure buildup within the overlying Kreyenhagen channel-fills. Intense grain microfracturing occurred during sand remobilization and injection along with erosion of the host mudrocks. This study has significance for the generation of reliable stratigraphic and petrological models for sand injection complex genesis and evolution that consequently can help the understanding and exploration of injectite complexes elsewhere.

Provenance of Pennsylvanian–Permian sedimentary rocks associated with the Ancestral Rocky Mountains orogeny in southwestern Laurentia: Implications for continental-scale Laurentian sediment transport systems

AbstractThe Ancestral Rocky Mountains system consists of a series of basement-cored uplifts and associated sedimentary basins that formed in southwestern Laurentia during Early Pennsylvanian–middle Permian time. This system was originally recognized by aprons of coarse, arkosic sandstone and conglomerate within the Paradox, Eagle, and Denver Basins, which surround the Front Range and Uncompahgre basement uplifts. However, substantial portions of Ancestral Rocky Mountain–adjacent basins are filled with carbonate or fine-grained quartzose material that is distinct from proximal arkosic rocks, and detrital zircon data from basins adjacent to the Ancestral Rocky Mountains have been interpreted to indicate that a substantial proportion of their clastic sediment was sourced from the Appalachian and/or Arctic orogenic belts and transported over long distances across Laurentia into Ancestral Rocky Mountain basins. In this study, we present new U-Pb detrital zircon data from 72 samples from strata within the Denver Basin, Eagle Basin, Paradox Basin, northern Arizona shelf, Pedregosa Basin, and Keeler–Lone Pine Basin spanning ∼50 m.y. and compare these to published data from 241 samples from across Laurentia. Traditional visual comparison and inverse modeling methods map sediment transport pathways within the Ancestral Rocky Mountains system and indicate that proximal basins were filled with detritus eroded from nearby basement uplifts, whereas distal portions of these basins were filled with a mix of local sediment and sediment derived from marginal Laurentian sources including the Arctic Ellesmerian orogen and possibly the northern Appalachian orogen. This sediment was transported to southwestern Laurentia via a ca. 2,000-km-long longshore and aeolian system analogous to the modern Namibian coast. Deformation of the Ancestral Rocky Mountains slowed in Permian time, reducing basinal accommodation and allowing marginal clastic sources to overwhelm the system.

Laboratory core investigations of sandstone-hosted uranium for in situ recovery

ABSTRACTSeveral core plugs from a 1243 m-deep borehole penetrating the Westwater Canyon Member of the Morrison Formation in New Mexico (USA) have been investigated by various petrophysical methods to evaluate the potential of extracting deeply buried sandstone-hosted uranium deposits by in situ recovery (ISR). Petrophysics and mineralization patterns of the host rock in the target aquifer are crucial parameters for ISR amenability and were determined according to the ISR feasibility criteria. Mineralogical investigations revealed a secondary uranium mineralization mainly coating the silica grains of the arkosic sandstone and some interstitial pore fillings. The differences between mineralized and non-mineralized sandstone plugs are highlighted by nuclear magnetic resonance (NMR), X-ray microcomputed tomography, and spectral induced polarization (SIP). The NMR results show a doubling of the clay- and capillary-bound water and a decease of free-fluid porosity of mineralized samples. A correlation of mineralization grade and polarization is observed through the SIP investigations.

Kremeňovo-karbonátové žily s U-Mo-Cu mineralizáciou v permských intermediárnych až bázických vulkanitoch hronika na lokalite Kravany (Kozie chrbty, východné Slovensko)

Historical uranium ore deposit Kravany is located in the eastern part of Kozie Chrbty Mts., approximately 9 km SW of the district town Poprad. Stratiform, infiltration U-Cu-Pb mineralization is bound to the Upper Permian clastic sediments (Kravany Beds, member of Malužiná Formation, Hronicum Unit), which are enriched in fragments of carbonized flora. Vein U-Mo-Cu mineralization was found in the Upper Permian intermediate to basic volcanics intersecting the sediments of the Kravany Beds (also ore lenses). Vein filling originated in the following development stages: I.) Quartz-pyrite (quartz, pyrite, marcasite), II.) Dolomite-pyrite (dolomite, pyrite, marcasite, galena), III.) Copper (tetrahedrite, tennantite, chalcopyrite), IV.) Uranium-molybdenum (uraninite, Pb-Mo-S phase, coffinite, quartz), and V.) Calcite (calcite, chalcopyrite). The formation of mineralization can be explained by the geological position: random emplacement of the diorite porphyrite, resp. basalt-andesite dikes, directly in the preexisting U,Mo-bearing sediments. Vein U-Mo-Cu mineralization could thus most likely have formed according to the following scenario: I.) sedimentation of Kravany Beds in the Permian riftogenic basin: formation of beds of arkoses and arkosic sandstones with abundant fragments of charred flora, II.) formation of infiltration U mineralization: reduction and accumulation of U in sediments rich in organic matter, III.) emplacement of dikes of intermediate to basic volcanics: intersection of sediments with organics and with high U and Mo content, mobilization of formation fluids, assimilation of U and Mo into intermediate-basic magma, IV.) cooling of volcanic bodies → their contraction (formation of contraction cracks) → filling of contraction cracks with quartz, carbonates and ore minerals (crystallization from residual magmatic solutions mixed with formation waters). From this point of view it is syngenetic volcanogenic vein U-Mo-Cu mineralization, originally of the Permian age, with subsequent Alpine (most probably Cretaceous) reworking (this is evidenced by the variable composition of uraninite). It belongs to the Neohercynian late- to postorogenic metallogenetic stage. The possible younger, post-Permian age of mineralization from alpine hydrothermal solutions must also be assumed, but this consideration has several inconsistencies.

Study on the lithofacies of the second member of Tengger formation in Jiergalangtu of Erlian Basin

Through analyzing coring well observation and in combination with drilling data log sheet and the analysis of the test data, combined with the regional sedimentary tectonic evolution background of the second member of Tengger formation in Jiergalangtu of Erlian basin, the results show that lithic arkose and feldspathic lithic sandstone are developed in the study area. There are abundant sedimentary structures, mainly including parallel bedding, laminated bedding and massive bedding, etc. According to the analysis of sedimentary characteristics, nine lithofacies types and four vertical assemblages are summarized, which respectively reflect different microfacies environments: subaqueous distributary channel subaqueous distributary channel interestuarine bar sheet sand.

Analysis of pore type and micro pore structure of reservoir in fault basin--Taking Wuerxun depression as an example

Wuerxun depression is the two main oil-bearing depressions in Hailaer basin. Nantun Formation of Wuerxun depression is the most important oil-gas exploration layer, and reservoir characteristics are the main factors controlling oil-gas enrichment. In this paper, the mineral composition and pore type of Nantun Formation reservoir are analyzed by XRD and SEM. It is clear that the main rock types are lithic sandstone and feldspar lithic sandstone. As a whole, it is compact, with poor connectivity of pores and coexistence of primary and secondary pores. Primary pore is mainly residual primary intergranular pore, and secondary pore is the main reservoir space of Nantun Formation, which lays a foundation for further oil and gas exploration. The rock types of the target layer in the study area are mainly lithic sandstone and feldspathic lithic sandstone. Among them, Tongbomiao formation in Wuerxun depression is dominated by conglomerate, while sandstone in Nantun Formation is mainly lithic arkose and feldspathic lithic sandstone; sandstone in Tongbomiao formation and Nantun Formation in Beier depression is dominated by lithic sandstone and feldspathic lithic sandstone. The rocks of Nantun Formation are compact as a whole, with poor connectivity of pores and coexistence of primary and secondary pores. The primary pores are mainly residual primary intergranular pores, mainly of three types. Secondary pore is the main reservoir space of Nantun Formation, including dissolution intergranular pore, dissolution intergranular pore, interstitial matter dissolution pore, intergranular micro pore and micro fracture of authigenic minerals, among which intergranular dissolution pore is the most developed and super large dissolution intergranular pore is the main one.

Supergénne minerály stratiformnej U-Cu mineralizácie pri Spišskej Teplici (hronikum, Kozie chrbty, východné Slovensko)

Occurrence of infiltration, stratiform U-Cu mineralization Spišská Teplica - Vápenica-Vysová is located approximately 7.8 km SW from the district town Poprad and 4.3 km SW from the centre of Spišská Teplica village (Slovak Republic). Primary U-Cu mineralization is bound to arkosic sandstones with abundant coalified fragments of higher plants (Kravany Beds, Upper Permian, Hronicum Unit) and consists of uraninite and pyrite. The chalcopyrite and Cu-S mineral phase (digenite?, roxbyite?) form inclusions in clastic fluorapatite and zircon. Among supergene minerals, malachite and goethite are absolutely dominant, azurite, zálesíite and baryte are less represented. Phosphate, probably of the florencite group, and acanthite were only rarely found. Supergene uranyl minerals were not detected. Their lack, or their weak development in all uranium deposits in Kozie Chrbty Mts. can be explained as follows: during the weathering of primary ores, the cation UO22+ is released from uraninite and coffinite into supergene solutions (uranyl complexes). However, these solutions come into almost immediate contact with fragments of coalified flora (especially in the case of rich U ores), where UO22+ binds to the organic uranyl complexes (complexation). Only a relatively small part of uranyl cation escapes from this geochemical trap, and in that case supergene uranium minerals may precipitate.

Phanerozoic Quartz Arenite Formation and Sequence-Analytical Patterns: Indirectly Relating to Major Impacting and Super Plume Volcanism, Jordan, Arabian Plate

This paper deals with indirect effects of major impacting throughout the Early Paleozoic resp. with those of super plume activity during the Early Cretaceous, both applied to the siliciclastic series of Jordan deposited on the Arabian Platform, Arabian Plate. Its focus is mainly directed on gases released by both processes (CO2, SO2, NOx, HCl, HF) and the relating acids, challenged by experiments and microscopic analysis of grain mounts and thin sections that reveal chemical instability of quartz and ultrastable heavy minerals (i.e. tourmaline) under high acidity (pH °C - 90°C). According to Lopatin’s Time/Temperatur-Index the Lower Cambrian reached the onset of hydrocarbon generation (liquid window) during the Lower Early Cretaceous. Unstable heavy minerals (apatite, garnet, hornblende, epidote, zoisite/clinozoisite) are generally absent in quartz arenites while in arkosic sandstones of marine environment carbonate cement and primary clay minerals (illite) provide conservation. As known since the eighties, the K/T-event’s indirect effects had global influence on Earth’s surface sediments and atmospheric chemistry by wildfires, hot whirl storms, acidic “sturz rain”, dust, soot, darkness, loss of photosynthesis, toxic metals, gases and relating acids. All of them are here concerned and applied to major impacting throughout the Early Paleozoic using the impact data of Price (2001); while superplume volcanism during Cretaceous led to the opening of the South Atlantic accompanied by the cyclic outflow of the Para?a/Etendeka Flood Basalts and relating gases in a gigantic scale (137 - 127 Ma). Assuming that the gases cause similar global effects on Earth’s surface sediments, an according result may be expected in form of quartz arenites and their sequence-analytical patterns (cyclic SBs, MFSs).*

Geology, alteration system, and uranium metallogenic potential of Pasha-Ladoga Basin, Russia

The Mesoproterozoic Pasha-Ladoga Basin is located at the margin of the Karelian Craton and Svecofennian Belt in northwest Russia. It is the only basin in Russia that is currently recognized to host unconformity-type uranium mineralization (e.g., Karku deposit). Mineralization is associated with the Priozersk Formation which comprises a basal sequence of immature arkosic sandstones and conglomerates interpreted as high-energy braided stream channel and channel bar facies within an alluvial fan depositional environment. Diagenetic and hydrothermal alteration of the Priozersk sandstones is similar to that observed in unconformity-related uranium deposits of the Athabasca Basin (Canada) and includes three main stages: (1) an early diagenetic assemblage comprising illite-smectite (K-rectorite), calcite, minor chlorite, and kaolinite precipitated at 100–150 °C; (2) a peak diagenetic-hydrothermal assemblage composed of kaolinite-dickite, Fe- and Fe-Mg chlorite, calcite, and sulfides formed at 150–250 °C; (3) late diagenetic-hydrothermal event involving fracture-controlled kaolinite and late hematite. Similar to the Athabasca Basin type uranium mineralization, the Karku deposit exhibits anomalous concentrations of LREE, Nb, Pb, and positive correlations between U and Cu, Zn, Ag, and Pb that is a geochemical signature of unconformity-type uranium mineralization. Based on oxygen and hydrogen stable isotope study, it was found that fluids in equilibrium with early and peak diagenetic clays were consistent with oxidized basinal brines and reduced basement fluids. In contrast to the Athabasca Basin, mineralizing fluids at the Karku area were more reduced and potassic. A new geological model for the Karku deposit is proposed based on petrographic observations and sandstones geochemistry. The proposed model envisages the permeable rocks of paleoregolith and the coarse-grained basal part of the Priozersk Formation as the main pathway for migration of uraniferous fluids responsible for the formation of Karku uranium deposit. From the perspective of the geological setting, the Karku deposit differs from deposits of the Athabasca Basin in that it occurs in a rapidly deposited rift-related basin with associated mafic magmatism, the host sandstone sequence is relatively thin (e.g., Priozersk Formation) and exhibits abrupt lateral facies variations, and the widespread presence of early diagenetic interstitial swelling clays. Based on these sedimentological characteristics, it is considered that the Karku deposit setting precludes optimum conditions to create high tonnage high-grade unconformity-type U deposits as found in the Athabasca basin.

Multimineral diagenetic forward modeling for reservoir quality prediction in complex siliciclastic reservoirs

Reservoir quality (RQ) prediction models for sandstones in use by the oil and gas industry primarily emulate mechanical compaction, quartz cementation, and cementation by a few select aluminosilicate minerals during burial. The modeled cements are treated on a kinetic basis using independent Arrhenius-style rate equations, and nonmodeled cements are constrained by empirical observations and data from analog rocks. The nonmodeled cements pose a significant modeling challenge in complex lithic and arkosic sandstones that contain carbonate, clay, or zeolite cements when analog data are not available for constraint. Twenty-nine samples covering a broad range of sandstone compositions were selected from four fields in four different sedimentary basins to investigate the potential of using modern reactive transport models (RTM) to simulate a more comprehensive suite of minerals involved in sandstone diagenesis. A commercially available RTM, GWB® X1t, was configured to model chemical diagenesis in a time–temperature burial framework conceptually similar to that employed in standard industry RQ forward models. Strategies were developed to consistently constrain kinetic parameters, fluid compositions, and fluid fluxes with the goal of standardizing these parameters to reduce configuration and calibration time. Results show that RTM using such standardized parameters can reproduce relative timing and volume changes caused by mineral dissolution and precipitation that are accurate within the uncertainty of the petrographic data constraint. The results suggest that incorporation of RTM into current industry models could provide a valuable improvement to siliciclastic RQ prediction in frontier plays with complex mineralogies wherever calibration data are sparse or unavailable.

Compositional evolution of siliciclastic sediments recording the tectonic stability of a pericratonic rift: Mesozoic Kutch Basin, western India

This study presents a combined petrographical and geochemical investigation to track the compositional changes in the Mesozoic sedimentary record during the evolution of the pericratonic rift basin of Kutch. The Mesozoic sequence of the proven petroliferous basin of Kutch, representing ~3000 m thick siliciclastic and carbonate deposition within a time frame of ~70 Ma, consists of Jhurio, Jhumara, Jhuran and Bhuj formations in ascending order of succession. The dominance of arkosic sandstones and the abundance of zircon and monazite indicate predominantly felsic source rocks. The concentration of individual trace elements such as Th, Sc, Zr, V, Ni and ratios like Th/Sc, Cr/V, Y/Ni, Th/Co, La/Sc support the predominantly felsic source rock. The LREE enrichment and the negative Eu anomaly corroborate the predominantly felsic source. However, concentrations of V, Ni and Ti reveal the mafic input in older stratigraphic units. While (GdN/YbN) indicates dominant post-Archean source across the Mesozoic succession, younger stratigraphic units reveal contributions from the Archean rocks, from Nagar Parkar and Aravalli highland regions. The CIA values suggest intermediate to intense weathering, while the ICV data record a shift from immature sediments in the older formations to mature and recycled types in the younger formations. The high value of Zr/Sc as well a high content of Hf reflects the addition of zircon by recycling or by erosional unroofing of older continental rocks. Major oxide (SiO2, Na2O and K2O) and trace elements (La, Th and Hf) bear the passive margin setting for the Kutch Basin during the Mesozoic. The decrease in feldspar content (in sandstones), increase in the concentration of Zr and Hf (in shale) and a decrease in values of ICV from older to younger stratigraphic units corresponds to the compositional evolution related to increased stability of the Kutch basin during the transition from early syn-rift to post-rift.